Sustainable assessment of an integrated energy system coupled with solar thermochemical cycle

The energy transition globally makes the development of carbon-free and low-carbon fuels obligatory as these fuels cannot only be utilized as energy carriers but also for long-term energy storage. This paper presents the energy, technoeconomic, and environmental assessment of a new hybrid renewable energy integrated system with a novel concept of the thermochemical cycle for methanol production. For this purpose, a thermochemical cycle based on CeO₂/Ce₂O₃ oxides is integrated with the methanol synthesis system. It consists of two chemical steps: (1) oxygen carrier reduction step where metal oxide reduction Ce (IV) to Ce (III) (endothermic phase) is performed employing renewable thermal energy and chemical energy originated from ultra-high concentrated photovoltaics and fossil methane respectively and (2) waste gas dissociation step where oxidation of Ce(III) takes place with dissociation of water and carbon dioxide (exothermic phase) and resulting syngas is converted to methanol. Plant design and simulation are performed in ASPEN plus commercial software. MATLAB was employed for the programming of thermal data to perform pinch analysis. The technical feasibility of the second step was investigated comprehensively in terms of temperature, input molar ratio and the potential operating conditions that were identified (T_OXI = 900 °C and H₂O/CO₂ = 3.7) based on methanol production performance. Overall energy efficiency, solar-to-fuel efficiency and thermal efficiency are calculated to be 77.2%, 38% and 44.1% respectively. The findings of the environmental analysis show that carbon utilization of 20.85%, carbon storage of 79.14%, carbon capture of 100% and carbon avoidance of 19.6% are achieved. Economic analysis shows that the net project capital expenditure (CAPEX) and operating expenditure (OPEX) are estimated to be $186.49M and $218.67M. It was found that the best-case scenario of natural gas (NG) price is 40$/MWh, where the breakeven point is achieved during the 5th year of the project lifetime.